High [CVE-2026-73500] Denial of Service via unbounded TLS handshake goroutines

etcd is a distributed key-value store for the data of a distributed system. Prior to versions 3.5.33, 3.6.14, and 3.7.1, a network attacker who can reach an etcd TLS listener can open many TCP connections and never send a ClientHello.

In client/pkg/transport/listener_tls.go, each connection handled by tlsListener.acceptLoop spawns a goroutine that blocks indefinitely inside tls. Conn.

Handshake() and remains tracked in the pending map.

Unbounded goroutine and map growth can exhaust memory in the etcd process, causing loss of availability for the cluster and, when etcd backs Kubernetes, the control plane. This issue is fixed in versions 3.5.33, 3.6.14, and 3.7.1.

A remote attacker can exploit this by opening numerous TCP connections to an etcd TLS listener without completing the TLS handshake. This action causes the `tlsListener.acceptLoop` to spawn an unbounded number of goroutines, which consume excessive memory.

This resource exhaustion leads to a Denial of Service (DoS) for the etcd cluster and, consequently, for the Kubernetes control plane it supports. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Weakness: CWE-770.

Affected products named by the advisory: Multicluster Global Hub; Red Hat Advanced Cluster Management for Kubernetes 2; Red Hat Ansible Automation Platform 2; Red Hat Ceph Storage 5; and 11 more.